1. Field of the Invention
The present invention relates to a boat for liquid phase epitaxial growth, and more particularly to an improvement for a boat for liquid phase epitaxial growth used in manufacturing a III - V group compound semiconductor.
2. Description of the Prior Art
The mass-production technique employing the liquid phase epitaxial technique is important in a semiconductor device using a III - V group compound semiconductor. The mass-production technique is particularly important in the field of GaAs solar battery with large sized device. A boat for liquid phase epitaxial growth used for manufacturing the GaAs solar battery by the liquid phase epitaxial method is disclosed in "Liquid Phase Epitaxy Technology of Large Area AlGaAs/GaAs Wafers of GaAs Solar Cells for Space Application", Yoshida et. al. The 17th IEEE Photovoltaic Specialists Conference Proceedings pp. 42-45, in which the authors propose a boat structure separated into three chambers, the epitaxial growth being carried out by transferring the crystal solution from an upper stage to a middle stage and then to a lower stage by means of sliders.
FIG. 1 is a cross sectional view of a conventional boat for liquid phase epitaxial growth used for manufacturing a GaAs solar battery or the like which requires mass-productivity.
In FIG. 1, a boat 1 for liquid phase epitaxial growth is of a 3-stage structure comprising an upper chamber 2, a middle chamber 3 and a bottom chamber 4. The upper chamber 2 is to reserve a solution 8 used for the liquid phase epitaxial growth. The middle chamber 3 is to contain a substrate 9 on which the liquid phase epitaxial growth is to be performed. The bottom chamber 4 is to contain the solution used for the liquid phase epitaxial growth, in which a drawer 5 is inserted. A slider 6 is interposed between the upper chamber 2 and the middle chamber 3 while a slider 7 is interposed between the middle chamber 3 and the bottom chamber 4. An opening 10 is provided in the slider 6 for introducing the solution 8 from the upper chamber 2 to the middle chamber 3. An opening 11 is provided in the slider 7 for introducing the solution 8 from the middle chamber 3 to the bottom chamber 4. In addition, a L shaped plate 12 is provided at the end of the slider 6, which moves the slider 7 in the direction of an arrow A in FIG. 1 with a predetermined delay from the time when the slider 6 is moved to the direction of the arrow A.
The operation of the conventional boat for liquid phase epitaxial growth shown in FIG. 1 will be described.
First, the boat 1 in the state of FIG. 1 is inserted into a furnace (not shown) and heated to the temperature for growth. When the temperature in the furnace reached a predetermined degree, the slider 6 is moved to the direction of the arrow A in FIG. 1, the solution 8 reserved in the upper chamber 2 is introduced to the middle chamber 3 through the opening 10 provided in the slider 6 and the substrate 9 is dipped in the solution 8. When the boat is gradually cooled as it is, an epitaxial layer grows on the surface of the substrate 9.
After the completion of the liquid phase epitaxial growth, the slider 6 is further moved to the direction of the arrow A to interlock the slider 7 by the L shaped plate 12 so that the opening 11 provided in the slider 7 is positioned below the middle chamber 3. Thus, the solution 8 flows from the middle chamber 3 into the bottom chamber 4 to be contained in the drawer 5.
Since the conventional boat for liquid phase epitaxial growth is structured as described above and the material of the boat is carbon, carbon powder is generated due to the sliding of the slider to contaminate the solution. In addition, solid oxide is included in the solution. In case where the solution including these carbon powder and oxide is employed, there arises a problem that the surface of the substrate becomes uneven causing degradation of the surface of the substrate finished with the liquid phase epitaxial growth.